Restrict registration by domain?

Is it possible to restrict WPAS user registration by email address domain?

I have a requirement to only all users from certain domains be able to open tickets.

I’ve tried to use a function like found on https://www.eyeswift.com/allow-registration-from-certain-email-domain-wordpress/ but I believe that function targets the WordPress site registration and not WPAS User Registration.

Has anyone done something similar? How’d you do it?